Automatic analyzers for conducting quantitative or qualitative analyses of particular components contained in a biological sample (blood, urine, etc.) have become indispensable for diagnosis today because of high reproducibility of analysis result, high processing speed, and so forth.
Measurement methods employed by the automatic analyzers are roughly classified into two types: an analysis method using a reagent that reacts with analysis-target constituents in the sample and thereby changes the color of the reaction solution (colorimetric analysis) and an analysis method using a reagent made by adding markers to substances that specifically react directly or indirectly with the analysis-target constituents and counting the number of the markers (immunity analysis). While the analysis in either analysis method is performed by mixing a prescribed amount of reagent into the sample, the mixture ratio between the sample and the reagent varies depending on the analysis item (analytical assay) and a relatively large sample suction (pipetting) quantity from approximately 1 μL to over 20 μL is necessary.
Generally, the automatic analyzer analyzes different samples for a plurality of analysis items. Thus the sample dispensation nozzle (for dispensing the samples) is cleaned for a period between the end of the pipetting of a sample and the start of the pipetting of the next sample and the carry-over between samples is prevented, whereby deterioration in the accuracy of the analysis is reduced.
Further, the automatic analyzer carries out the analysis by programming the sample dispensation and the cleaning in one operation cycle and repeating such an operation cycle. The contaminated region in the nozzle increases especially when the sample suction quantity (quantity of the sample sucked into the nozzle) is large. Thus, in order to sufficiently perform the nozzle cleaning, Patent Document 1 describes a method in which the nozzle cleaning time (duration) is changed based on the type or the dispensation quantity of the sample.